Method of controllably delivering dopant by limiting the release rate of dopant from a submerged vessel

ABSTRACT

A time-released dopant delivery system and method are provided in a Czochralski-type crystal-growing furnace to enable continuous doping of the melt over time. The dopant delivery system and method adjusts dopant levels within the melt as a function of time such that a controlled amount of dopant and, more typically, a substantially constant amount of dopant can be incorporated into the ingot over its length. By controlling the doping level in the ingot, the resistivity profile of the ingot can also be controlled over its length. In order to provide controlled dopant delivery, the dopant delivery system generally includes a vessel defining an internal cavity within which the dopant is disposed and an orifice through which the dopant, typically a molten dopant, is released. The dopant delivery system can also include means for submerging the vessel within the melt such that heat from the melt melts and therefore releases the dopant into the melt. Alternatively, the vessel can be at least partially defined by the crucible so as to be disposed within the melt. By properly configuring the orifice defined by the vessel, however, the release of dopant into the melt can be regulated.

RELATED APPLICATION

The present application is a divisional of U.S. patent application Ser.No. 09/241,874, filed Feb. 2, 1999, now U.S. Pat. No. 6,179,914 B1entitled DOPANT DELIVERY SYSTEM AND METHOD.

FIELD OF THE INVENTION

The present invention relates generally to the growth of dopedsemiconductor crystals and, more particularly, to the controlleddelivery of dopant to a molten host material contained within a meltcrucible in a crystal-growing furnace.

BACKGROUND OF THE INVENTION

Current methods of growing single crystal ingots in a Czochralski-typecrystal-growing furnace typically involve melting a polycrystalline hostmaterial, such as silicon, and a measured amount of dopant together in acrucible to create a melt. Once the melt is prepared, a seed crystal islowered into contact with the melt to begin the crystal-growing process.As the seed crystal is slowly extracted from the melt, a monocrystallinecrystal or ingot is drawn from the melt. Unfortunately, themonocrystalline ingot does not necessarily include a proportionate shareof the dopant in the melt. Instead, the percentage of dopantincorporated into the monocrystalline ingot depends on the applicablesegregation coefficient and other parameters.

Typically, the ingot incorporates a smaller percentage of the dopantthan the melt. As such, the dopant concentration in the melt willincrease over the crystal-growing period as the ingot is drawn from themelt. Due to the increasing dopant concentration in the melt, the ingotwill also gradually incorporate a larger amount of dopant as the growthprocess proceeds. Since the resistivity of the ingot is a function ofthe amount of incorporated dopant, ingots that incorporate a increasingamount of dopant over their length also have a resistivity thatdecreases over their length. As a result, the wafers into which an ingotis sliced will also have slightly different resistivities depending uponthe relative lengthwise location from which each wafer was sliced. Sincepurchasers of the wafers typically specify an acceptable range ofresistivity values depending upon the intended use of the wafer, only asubset of the wafers harvested from an ingot may satisfy therequirements imposed by a purchaser.

U.S. Pat. No. 5,406,905 to Yemane-Berhane et al. discloses a techniquefor doping the melt after the host material has been melted in thecrystal-growing furnace. This technique involves casting the dopantaround the seed crystal used to grow the ingot. When the furnace isprepared, the dopant-coated seed crystal is held in a relatively coolpart of the furnace until the host material has melted and is ready fordoping. The dopant-coated seed crystal is then lowered to a positionjust above the melt. Heat transferred from the melt to the dopant-coatedseed crystal causes the dopant, in solid form, to slip off the seedcrystal and into the melt, hopefully without splashing and withoutimmersing the seed crystal in the melt.

However, the '905 Yemane-Berhane et al. patent does not address theproblems associated with variations in the concentration of the dopantthroughout the course of drawing an ingot from the melt. Instead, whenthe temperature of the seed crystal rises due to the heat from the melt,a point is attained where the dopant will slide off the seed. Here, allof the dopant is delivered to the melt before the seed crystal isimmersed in the melt to begin the ingot growing process. Thus, thistechnique is still prone to the problem of the conventional techniqueswherein, as the crystal is grown, the concentration of the dopant in themelt will continually change, thereby altering the resistivity profileof the ingot in a lengthwise direction.

U.S. Pat. No. 5,242,531 to Klingshirn et al. discloses a process forcontinuously recharging a melt crucible with additional molten hostmaterial and additional molten dopant. In this regard, the Klingshirn'531 et al. patent describes separate containers filled with the hostmaterial and the dopant that are positioned above the melt crucible.Feedlines connect the containers with an additional crucible orcontainer in which the host material and the dopant are mixed andmelted. This additional crucible includes an outlet for supplyingadditional molten semiconductor material to the melt in order torecharge the melt during the crystal-growing process. While the '531Klingshirn et al. patent addresses some of the issues with respect tocontrolling the amount of dopant in the melt throughout the course of acrystal-growing process, the technique described by the '531 Kingshirnet al. patent requires multiple containers positioned above the meltcrucible which may complicate the design of the crystal-growing furnaceand limit access to the melt crucible during the crystal-growingprocess.

Therefore, a need still exists for improved techniques of controllingthe amount of dopant in the melt throughout the course of thecrystal-growing process without requiring significant modifications tothe crystal-growing furnace and without incurring the attendant costs.Consequently, a need still exists for improved techniques forcontrolling the concentration of dopant incorporated into the ingot overthe length of the ingot, thereby also permitting the resistivity of theresulting wafers to be controlled.

SUMMARY OF THE INVENTION

The dopant delivery apparatus and associated method of the presentinvention effectively control the amount of dopant in the meltthroughout the course of a crystal-growing process such that theconcentration of dopant incorporated into the resulting ingot can becontrolled over the length of the ingot. As such, the resistivity of theresulting wafers is also controlled, thereby overcoming the shortcomingsof conventional crystal-growing processes. According to the presentinvention, an apparatus is provided for controllably delivering dopantto a melt which includes a vessel disposed in the melt and defining aninterior cavity for containing the dopant. The vessel also defines atleast one output orifice through which molten dopant is released intothe melt, albeit at a release rate limited by the configuration of theoutput orifice. By regulating the release rate of the molten dopant intothe melt, the dopant delivery apparatus precisely controls the overallconcentration of dopant during the course of the crystal-growingprocess. In this fashion, the concentration of dopant incorporated intothe ingot is also controlled over the length of the ingot such that theresulting wafers can have precisely defined resistivity characteristics.

In one embodiment, the dopant delivery apparatus is a submergible vesselhaving a housing defining the interior cavity and the orifice throughwhich the molten dopant is released into the melt. The submergiblevessel of this embodiment also includes means for submerging the housingwithin the melt. For example, the means for submerging the housing caninclude a weight positioned within the housing. In one advantageousembodiment, the housing is a capsule having a substantially cylindricalbody and two opposed closed ends. According to this embodiment, one ofthe enclosed ends is weighted such that the capsular housing standssubstantially vertical when immersed in the melt. According to anotherembodiment, the housing of the submergible vessel is a truncated capsulehaving an open end and an opposed closed end. According to thisembodiment, the closed end is weighted such that the truncated capsularhousing stands substantially vertical when immersed in the melt. Assuch, the open end of the truncated capsular housing serves as theorifice through which the molten dopant is released. The truncatedcapsular housing can also include baffles affixed to an interior surfaceof the housing and extending into the interior cavity for controllingthe mixing of the melt with the dopant.

According to another embodiment, the vessel is not only submerged withinthe melt, but is secured within the melt crucible. More particularly,the vessel can be at least partially defined by the melt crucible,preferably in a position that is aligned with the crystal drawn from themelt. The vessel of this embodiment can also include a lid which isremovably attached to the melt crucible so as to cover the portion ofthe vessel destined by the melt crucible. Preferably, the lid defines atleast one output orifice that is sized to regulate the release rate ofthe dopant.

In operation, dopant is disposed within the vessel, typically in a solidform. As described above, the vessel is positioned within the melt tooperatively enable release of the dopant through the output orifice andinto the melt. In one embodiment, for example, the vessel is positionedin an aligned relationship with respect to the crystal drawn from themelt. In any event, the heat from the melt melts the dopant which isthereafter released through the orifice defined by the vessel. Inparticular, a portion of the melt generally enters the vessel andbecomes supersaturated with dopant such that the subsequent release ofthe supersaturated melt from the vessel through the output orificecontrollably dopes the remainder of the melt. In order to grow ingotsthat include precise concentrations of two or more dopants, the dopantdelivery apparatus and method of the present invention can include twoor more vessels positioned within the melt so as to controllablyintroduce different dopants throughout the course of the crystal-growingprocess.

According to the present invention, the release rate of the dopant islimited by the configuration of the output orifice, i.e., the size andshape of the orifice. As such, the amount of dopant introduced into themelt throughout the course of the crystal-growing process can beprecisely controlled such that the concentration of dopant in the meltand, in turn, the concentration of the dopant incorporated into theingot can be controlled over the length of the ingot, thereby enablingcontrol of the resistivity of the resulting wafers sliced from theingot. Still further, the dopant delivery apparatus and method cancontrollably release more or less dopant into the melt during the courseof the crystal-growing process if it is desired to change the dopantconcentration in the tail portion of the ingot in comparison to the headportion of the ingot. In any event, the dopant delivery apparatus andmethod of the present invention permits the concentration of dopantincorporated into the ingot to be more precisely controlled.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of one embodiment of the present invention whereinthe dopant delivery system includes a submergible vessel that is fullysubmerged in the melt.

FIG. 2 is a cross-sectional side view of the submergible vesselaccording to one embodiment of the present invention.

FIG. 3 is a cross-sectional side view of the submergible vessel of analternative embodiment of the present invention.

FIG. 4 is a side view of an alternative embodiment of the presentinvention wherein the melt crucible at least partially defines thevessel.

FIG. 5 is a flowchart of the operations performed by the dopant deliverysystem and method of one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout.

In a typical Czochralski-type semiconductor crystal-growing furnace, apolycrystalline host material, such as silicon, and a measured amount ofdopant are melted together in a crucible. The dopant is generally eitheran n-type or a p-type dopant, such as phosphorus or boron, respectively.Once the melt is prepared, a seed crystal is lowered into contact withthe melt to begin the crystal-growing process. As the seed crystal isslowly extracted from the melt, a monocrystalline crystal or ingot isdrawn from the melt which incorporates a certain percentage of thedopant. The percentage of dopant incorporated into the ingot depends onthe applicable segregation coefficient and other parameters as known tothose skilled in the art.

According to some conventional crystal-growing processes, the ingot mayincorporate a smaller percentage of dopant than the melt such that thedopant concentration in the melt will gradually increase as the ingot isdrawn from the melt. Therefore, an increasingly greater amount of dopantwill be incorporated into the ingot as this type of growth processproceeds. Consequently, the resistivity profile of the resulting ingotwill vary over its length.

The dopant delivery system and method of the present invention istherefore particularly adapted to overcome the shortcomings ofconventional crystal-growing methods by controlling, as a function oftime, the delivery of dopant to a melt contained within a melt cruciblein a crystal-growing furnace. As explained below, this dopant deliverytechnique can help to prevent the change in concentration of the dopantin the melt as the ingot is grown. In other words, the controlleddelivery of dopant according to the present invention permits continuousdoping of the melt over time, thereby controlling the dopantconcentration in the melt. By controlling the dopant concentration inthe melt, the resistivity profile of the ingot can be preciselycontrolled, such as by being held more uniform over the length of theingot or being changed in a controlled fashion over the length of theingot, thereby generally resulting in a greater usable yield and higherefficiency for a crystal-growing process incorporating the presentinvention.

Referring now to the drawings, FIG. 1 shows one embodiment of the timereleased dopant delivery system of the present invention, indicatedgenerally by the numeral 70, for controllably delivering dopant to amelt during the course of a crystal-pulling process. A typicalCzochralski-type crystal growth furnace includes a susceptor 12,typically formed of graphite, and a crucible 15, typically formed ofsilicon, seated within the susceptor for containing the melt 20 fromwhich a crystal or ingot 25 is grown. The melt is typically formed bymelting a mixture of host material, such as silicon, and a predeterminedamount of dopant together in the crucible. The dopant may be anysuitable dopant.

The dopant delivery system 70 of the present invention includes a vesseldisposed in the melt that defines an interior cavity for containing asolid dopant. As shown in FIG. 2, the dopant delivery system of oneadvantageous embodiment includes a submergible vessel 75. That vessel isconstructed of a material, such as quartz or any other suitablematerial, capable of withstanding temperatures greater than thetemperature of the melt. According to this embodiment, the dopantdelivery system also includes means for submerging the vessel within themelt. For example, the vessel 75 may incorporate the submersion means bybeing constructed so as to have sufficient weight to sink below thesurface of the melt. For instance, the walls of the vessel could besufficiently thick to provide the required weight or the vessel couldcontain an internal weight 85. As shown in FIGS. 1 and 2 and asdescribed in more detail below, the vessel also defines an outputorifice 80 through which dopant, typically in a molten form, is releasedinto the melt at a release rate limited by the configuration of theoutput orifice.

Once the vessel 75 is submerged in the melt 20, various factorscontribute to facilitate the controlled release of dopant 40 into themelt 20. In particular, the thermal energy of the melt 20, theconfiguration of the vessel 75, and/or the configuration of the outputorifice 80 generally cooperate to control the release of dopant 40 intothe melt 20. In this regard, the dopant generally gradually melts as aresult of the thermal energy emitted by the melt 20. Alternatively, thevessel 30 may have a built-in source of thermal energy for melting thedopant 40 contained therein. Still further, the vessel may be initiallyloaded with a molten dopant, but the orifice 80 may be opened, such asby thermal activation, only after properly positioning the vessel withrespect to the melt. In any event, once the vessel is properlypositioned and the dopant is melted, the dopant 40 will flow through theorifice 80 and into the melt 20, thereby controllably changing thedopant concentration in the melt 20 as a function of time.

The orifice 80 can be defined by a valve or the like to permit theoutflow of dopant 40 from the vessel 75 while preventing the flow of themelt 20 into the vessel. Typically, however, the orifice 80 is open soas to allow the passage of the melt 20 into the vessel 75. Once the melt20 enters the vessel 75 through the orifice 80, the melt liquefies anyremaining solid dopant and forms a supersaturated solution of dopant inmelt. The supersaturated solution then flows from the vessel 75 anddopes the melt 20 as it is released and remixed with the remainder ofthe melt 20 in the crucible 15. However, the amount of supersaturatedsolution and, more particularly, the amount of melted dopant that isreleased into the melt 20 is limited by the size of the orifice 80,thereby controlling the rate at which the melt is doped.

In a further example, the dopant 40 contained within the vessel 75 couldbe designed to have specific melting characteristics. For instance, ifthe mass of solid dopant 40 was a square or rectangular block which wasconstrained to have only two opposing faces exposed to the thermalenergy from the melt 20, the exposed surface area would be constant overtime. Thus, the amount of dopant melting at any time would be constantand, as such, the release rate of the dopant 40 from the vessel 75 wouldbe substantially linear. Alternatively, the dopant mass could bestratified, wherein the different strata could have differing densitiesor different compositions, each exhibiting different melting properties.It should be apparent to one skilled in the art that there are variousways to selectively control the melting properties of a mass, of whichthe above are illustrations.

In still a further alternative, the vessel 75 may define at least oneinput orifice, in addition to the output orifice 80, to furtherfacilitate the flow of the melt 20 into the vessel 75. A supersaturatedsolution of dopant in melt is then formed as described above for releaseinto the melt 20 through the output orifice 80 to dope the remainingmelt. The dopant delivery system 70 of the present invention thereforepermits additional dopant to be controllably added to the melt duringthe course of a crystal-pulling process. As such, the dopant deliverysystem can add more of the same dopant with which the melt is alreadydoped and/or can add other dopant(s), if so desired.

The vessel 75 can have any of a variety of shapes without departing fromthe spirit and scope of the present invention. As shown in FIGS. 1 and2, for example, the vessel of one embodiment is a capsular housinghaving a substantially cylindrical portion 95 with hemispherical closedends 100 and 105. The dopant delivery system 70 of this embodiment alsoincludes a weight 85 positioned within the vessel. For example, one endof the vessel can be weighted such that the weighted end 100 is biasedtoward the bottom of the crucible 15 and the vessel 75 standssubstantially upright when the vessel is immersed in the melt 20.Formation of the weighted end 100 can be accomplished, for example, byconstructing the vessel 75 with a thicker wall at the weighted end 100or by adding a weight 85 to the vessel 90. As shown, the cylindricalportion 95 of the vessel defines an output orifice 80 while theunweighted end 105 may define a gas escape orifice 120 to release anyair trapped in the vessel 75 or gas produced by the melting dopant.Although the orifices can be defined in a variety of locations, thevessel of one advantageous which defines an axis 75′ extending thoughthe two opposed closed ends preferably defines the output orifice suchthat a central axis 80′ defined so as to extend through the outputorifice is perpendicular to the axis defined by the vessel. In addition,the vessel of this embodiment can define the gas escape orifice 120 soas to be disposed along the axis defined by the vessel.

The vessel 75 can be loaded with dopant 40 in a variety of manners. Inthe embodiment illustrated in FIG. 2. however, the capsular housingincludes first and second portions which can be threadably engaged byrespective threaded portions 90. As such, the first and second portionscan be separated and filled with dopant. Thereafter, the first andsecond portions can be threadably connected to form the capsular housingin which the dopant is disposed.

Once submerged in the melt 20, the thermal energy of the melt melts thedopant 40 within the vessel 75 such that a solution supersaturated withdopant is released into the melt 20 through the output orifice 80. Atthe output orifice, a localized supersaturation of dopant in melt istherefore formed. However, due to the rotation of the crucible 15 andthe viscosity of the melt 20, a rotational motion is also imparted tothe vessel 75, thereby mixing of the released dopant with the melt 20.As a result, the amount of dopant 40 delivered to the growing ingot 25can thereby be controlled so as to allow for more precise resistivitycharacteristics throughout the ingot 25.

Now referring to FIG. 3, an alternate embodiment of the vessel is shownas indicated generally by the numeral 130. In this embodiment, thevessel 130 comprises a cylindrical portion 135 with a singlehemispherical closed end 140. The closed end 140 is weighted to bias thevessel 130 into an upright position with the weighted end at the bottomof the crucible 15. Formation oil the weighted end 140 can beaccomplished, for example, by constructing the vessel 130 with a thickerwall at the weighted end 140 or by adding a separate weight 145 to thevessel 130. The vessel 130 also contains one or more internal baffles150 affixed to the inner wall of the vessel 130 and extending into theinternal cavity. The baffles 150 serve to control the mixing of thedopant 40 with the melt 20. The cylindrical portion 135 further definesan open end 155, opposite the closed end 140, which serves as the outputorifice.

Accordingly, when the vessel 130 containing dopant 40 is submerged inthe melt 20, a portion of the melt 20 enters the vessel 130 through theopen end 155. As with the previous embodiment of the vessel shown inFIG. 2, the rotation of the crucible 15 and the viscosity of the melt 20impart motion to the submerged vessel 130 while the thermal energy ofthe melt 20 melts the dopant 40 and forms a localized supersaturatedmixture of dopant in melt within the vessel. The baffles 150 in thevessel 130 serve to further mix the dopant 40 and the melt 20. Once thesupersaturated mixture forms within the vessel 130, it is released backthrough the open end 155 of the vessel to mix with the remainder of themelt 20 as described above.

As shown in FIG. 4, the vessel can be secured within the melt crucible15. While the vessel can be positioned in different locations within themelt crucible, the vessel of one advantageous embodiment is aligned withthe crystal ingot 25 that is drawn from the melt such that the dopantreleased by the vessel will be evenly distributed throughout the meltrelative to the crystal ingot. In the embodiment illustrated in FIG. 4,the vessel 160 is at least partially defined by the melt crucible 15. Inparticular, the melt crucible of this embodiment can define thegenerally cup-shaped recess for receiving and storing the dopant. Thevessel of this embodiment can also include a lid 165 which covers theportion of the vessel defined by the melt crucible. Typically, the lidis removably connected to the melt crucible, such as by means of athreaded connection or the like, such that the lid can be removed inorder to fill the vessel with dopant. As shown, the lid also defines oneor more output orifices 170 through which the molten dopant is released.As described above in conjunction with other embodiments of the vessel,the release rate of the dopant is limited by the configuration, i.e.,the shape and size, of the output orifices defines by the lid.

Now referring to FIG. 5, a flowchart illustrating the operationsperformed by the dopant delivery system and method of the presentinvention is shown. Initially, as shown in block 200, the dopantdelivery system and, more particularly, the vessel is loaded with theproper dopant for the particular application. As described above, thedopant loaded in the vessel can be either identical to the dopant withwhich the host material is doped so as to supplement the dopingconcentration over time or different than the dopant with which the hostmaterial is doped so as to controllably dope the resulting ingot withtwo different dopants.

Once the furnace is prepared as shown in block 210, the next steps, asshown in blocks 220 and 230, are to coordinate the start of the crystalgrowth process with the activation of the time released dopant deliverysystem. For example, the dopant delivery system can be immersed withinthe melt either before or after the seed crystal is lowered into contactwith the melt. In instances in which the dopant delivery system isimmersed within the melt before the seed crystal is lowered into contactwith the melt, the dopant delivery system can be inserted into the melteither after the initial charge has been melted or prior to melting theinitial charge. As indicated by FIG. 5, however, the dopant deliverysystem, such as the submergible vessel, is typically immersed within themelt prior to lowering the seed crystal into contact with the melt andbeginning the crystal-growth process. The ingot is then drawn withadditional dopant added to the melt by the dopant delivery system andmethod, as described above. Once the desired ingot is obtained, theingot pulling process ceases as shown in block 240. By controllablyadding dopant throughout the pulling process, the resistivity profile ofthe ingot can be precisely controlled, such as by being held moreuniform over the length of the ingot or being changed in a controlledfashion over the length of the ingot. As such, the dopant deliveryapparatus and method of the present invention generally increases theyield and, correspondingly, the efficiency of a crystal-growing processsince the resulting ingots will have more precisely tailored properties.

Although the dopant delivery system method of the present invention hasbeen described hereinafter in conjunction with a single vessel forintroducing dopant into the melt, the dopant delivery system method ofthe present invention also contemplates the introduction of two or morevessels into the melt in order to controllably introduce two or moredifferent dopants into the melt throughout the course of thecrystal-growing process. As such, the resultant crystal ingot can becontrollably doped with multiple dopant, if so desired.

Many modifications and other embodiments of the invention will come tomind to one skilled in the art to which this invention pertains havingthe benefit of the teachings presented in the foregoing descriptions andthe associated drawings. Therefore, it is to be understood that theinvention is not to be limited to the specific embodiments disclosed andthat the modifications and other embodiments are intended to be includedwithin the scope of the appended claims. Although specific terms areemployed herein, they are used in a generic and descriptive sense onlyand not for purposes of limitation.

That which is claimed:
 1. A method of controllably delivering dopant toa melt contained within a melt crucible in a crystal-growing furnace,comprising the steps of: disposing a dopant within a vessel, said vesseldefining at least one output orifice; positioning said vessel in themelt within the melt crucible to enable release of the dopant from saidat least one output orifice into the melt; wherein positioning saidvessel in the melt comprises permitting said vessel to move freelywithin the melt; and limiting the release rate of the dopant throughsaid at least one output orifice into the melt, wherein said releaserate of the dopant is limited by a configuration of said at least oneoutput orifice.
 2. A method according to claim 1 wherein the step ofpositioning said vessel comprises aligning said vessel with the crystaldrawn from the melt.
 3. A method according to claim 1 further comprisingthe steps of: disposing a second dopant within a second vessel, saidsecond vessel defining at least one output orifice; and positioning saidsecond vessel in the melt within the melt crucible to enable release ofthe second dopant from said at least one output orifice and into themelt such that at least two dopants are delivered to the melt.
 4. Amethod of controllably delivering dopant to a melt contained within amelt crucible in a crystal-growing furnace, comprising the steps of:disposing, a dopant within a vessel, said vessel defining at least oneoutput orifice; positioning said vessel in the melt within the meltcrucible to enable release of the dopant from said at least one outputorifice into the melt, wherein the step of positioning said vesselcomprises immersing said vessel in the melt such that a portion of themelt enters the vessel and becomes supersaturated with the dopantcontained therein; and releasing the supersaturated melt from the vesselthrough said at last one output orifice to recombine with other portionsof the melt, wherein releasing the supersaturated melt compriseslimiting the release rate of the dopant through said at least one outputorifice into the melt based upon a configuration of said at least oneoutput orifice.
 5. A method according to claim 4 wherein the dopant isin a solid form at least initially upon positioning the vessel in themelt, and wherein the method further comprises permitting contactbetween the melt and the solid form of the dopant once the vessel ispositioned in the melt.
 6. A method of controllably delivering dopant toa melt contained within a melt crucible in a crystal-growing furnace,comprising the steps of: disposing a dopant within a vessel, said vesseldefining an internal cavity and at least one output orifice opening intothe internal cavity; positioning said vessel in the melt within the meltcrucible to enable release of the dopant from said at least one outputorifice into the melt, wherein positioning said vessel in the meltcomprises submerging said vessel within the melt such that every openingto the internal cavity defined by said vessel is beneath a surface ofthe melt; and releasing dopant into the melt through said at least oneoutput orifice.
 7. A method according to claim 6 wherein releasingdopant comprising limiting the release rate of the dopant through saidat least one output orifice into the melt, wherein said release rate ofthe dopant is limited by a configuration of said at least one outputorifice.